It doesn't matter whether it's good writing or bad as both are still part of the plot. So it's completely redundant to consider specific parts the result of the 'plot' as that implies that others are not, which is not the case. A character that beats another character and saying that he could only have beaten him because of a plotshield, well likewise it was that same plotshield that made that character that powerful in the first place. Making a character powerful and consequently let him be beaten with a supposed plotshield, well then that plotshield was the result of what could be considered creating a bad written powerful character. If you create a powerful character and then do not know how it has to be beaten, well then that character is likewise bad. They are connected, the plot is one whole, one entity, so saying that one thing is plotshield, but another thing that is directly connected to it is not, well that's wrong. Then you are dividing something that is a single entity into different subjective compartments.
Reality is that the whole Bleach manga can be considered not to have been written particularly great and the entire Quincy arc in particular, but that's just my opinion. In the end a character being ridiculously powerful as a result of nothing else than the creator writing him like that, is the same thing as that same character being beaten by another character that gets a friendship boost. Where did Bach's power come from in the first place? Kubo's pen, the same thing that will produce his downfall.
